Platinum-group metal sheet



31,166,417 Patentedjan. 19, 1965 United States Patent Ofi ice 3,166,417 PLATINUM-GROUP METAL SHEET Peter Edward Gainsbur-y, Ruislip, England, assignor to The InternationaiNickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. I Filed Apr. 29, 1963, Ser. No. 276,187

Claims priority, application Great Britain, May 7, E62,

. Claims. (Cl. 75-406) The present invention relates to a process for producing platinum-group metal in sheet or strip form and, more particularly, 'to a process for producing platinum and alloys thereof in sheet form.

' It is known to produce sheet or strip of a malleable metal of the platinum group, e.g., platinum, palladium, rhodium and alloys thereof, containing at least about 50% of metal from the platinum group, by casting the metal and workingthe cast piece. However, the worked 'metal generally has a relatively low recrystallization temperature with the result that it haspoor strength when subjected to high temperature, e.g., 1200 C. Prior known powder metallurgical methods, which result in a wrought platinum-group metal having a higher recrystallization temperature than obtainable with wrought and cast metal, have required extensive working of sintered compacts. It is advantageous to provide a powder metallurgical method which results in the desired product having a high recrystallization temperature while at the same time does not require extensive cold working. Although many .attempts were made to provide such an advantageous method, none as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by specially controlling the type of platinum-group metal powder employed in a powder metallurgical process together with controlling the processing conditions to which said powder is subjected during said process, advantageous sheet products including strip can be formed without the need for extensive cold working.

i It is an object of the present invention to provide a novel powder metallurgical process. Another object of the invention is to provide a novel 'powder metallurgical processfor the manufacture of dispersionehardened platinum-group metals.

The invention also contemplates providing a novel dispersion-hardened platinum-group metal sheet product.

Other objects and advantages will become apparent from the 'following'descriptioni r The present invention relates to a new process of producing sheet or strip. of a platinum-group metal or an alloy thereof. The sheet or strip metalhas a raised recrystallization temperature and its strengthis maintained at 1200" C. and above. The products do not require extensive working. Broadly, theinvention comprises forminga; compact of flake powder of a metal of the platinum group, heating the compact to' a temperature such that the flakes are sintered to a continuous mass and subsequently working thelsintered metal to yield sheet or strip metal, the working being efl ected either in the coldwith fintersta'ge annealing orby 'hotworking This working also consolidates the sintered compact to provide a prodnot having substantially 100% theoretical density.

Flake powder is conveniently made by stamping in a multiple stamp mill or by ball-milling conventional granular powder with steel balls in the presence of a trace of stearic acid' as a lubricant. It is a powder the particles of which are in the form of flakes a major portion of which has an .average particle size such that its maximum length or width is about 100 microns and a thickness of the order of about 1 micron. It is believed that the particular advantages achieved by the use of such a powder are caused by the orientation of the flakes in a plane parallel to the surface during sintering.

The sintering temperatures of platinum-metal flakes are similar'to normal powders of these metals and, in general, a temperature of at least 800 C. is required. 1000 C. is a convenient temperature at which to sinter platinum and palladium but considerably higher temperatures can be necessary for the other platinum metals.

The invention is particularly applicable to the production of dispersion-hardened products. As is known to those skilled in the art, dispersion-hardened metals comprise a matrix of metal throughout which an'extremely finely divided, hard non-metallic phase is dispersed. The non-metallic phase can consist of thoria, alumina, zirconia, etc. In general, the non-metallic phase consists of oxidic or other particles which are thermodynamically stable with respect to the matrix metal at temperatures encountered in production anduse. For malleable metals of the platinum group, inclusive, from the practical 'metals with each other-and/or with other metals such as gold, silver, nickel, copper and the like. As in non-dispersion-hardened systems, the platinum metal alloys with said other metals contain alloying amounts, e.g., greater than about O,5% and up to about 40% or 50% by weight of one or more of said other metals with the balance of the alloys being at least one of the malleable platinumgroup metals'in a major amount, that is, in an amount of at least about 5.0% ofthe total weight of the alloy metal.

In one way of carrying out the invention, the compact isformed by filling an appropriate mold with the flake powder and applying considerable pressure, for example, hydraulically, so that the powder forms a self-supporting piece which can subsequently be removed from the mold and sintered.

According to another method of carrying out the invention a compact is formed by applying to an inert support a paste of the flake powder in a liquid which will volatilize or decompose under heat, the nature of the support being such that the flake powder when sintered will not adhere to it. By forming a piaste of the flake powder, the flakes are brought into intimate contact with each other and can thus be regarded as having formed a cornpact even though the paste as such is not self-supporting. In fact, a compact within the accepted more. limited sense of the Word is formed as soon as the liquid in the paste is volatilized or decomposed by'heating. In practice, the

heating of the. flake powder paste on the surface of the volatilized or decomposed. by gentle heating 'to prevent blistering of the coating and at the end of this stagethe flakepowder is truly a compact, In the second stage, that of sintering, strongheating is used. It is convenient to use a two-part mold, since the surround (i.e., that portion of the mold. defining the yertical walls of themold cavity) may then be removed after the liquid component has been volatilized or decomposed and the metal residue has become suthciently coherent to remain in place. The strong heating. maythenl be carried out and finally the sintered metal removed. for coldbrhot working. By this method it is possible to use a metal surround for the mold. This should, of course, withstand the temperature at which initial cohesion of the flakes occurs and suitable materials are brass, aluminum and copper.

If the compact is to be formed by applying a paste to an inert support, it follows that the invention can be carried out only on supports which will withstand the high temperature necessary for sintering, i.e., 800 C. and higher. The inert support to which the paste is applied must not soften or exude a glaze when heated to the sintering temperature of the flake powder. Its surface must not be covered with a glaze which melts or softens when so heated and it must not react with the flake powder at the sintering temperature in the atmosphere in which heating is effected. Suitable materials from which the support can be made are alumina, unglazed porcelain and zircon. Ceramics containing easily reducible constituents such as silica should not be used in a reducing atmosphere because then the flake metal powder may adhere to the support. The support conveniently forms the base of a two-part mold comprising a detachable surround and a base. Alternatively, the paste may be extruded or rolled on to the surface of the support and in such a case there is no need to use a surround.

The liquid constituent of the metal-containing paste can be any that will volatilize or decompose on being heated. It can be water but advantageously is a resin dissolved in an organic solvent, e.g., an alkaline condensed methanol methyl cyclohexanone polymer dissolved in toluene or 2-ethoxy ethanol, diacetone alcohol, Z-ethoxy acetate or similar solvent. In the preparation of other than small thickness compacts, i.e., below about 5 mm. thickness, toluene is to be preferred since it is desirable that the solvent should have a boiling point below the melting point of the resin constituent, otherwise a resin skin is liable to form which inhibits the elimination of the medum. Alternatively, for small thickness compacts the resin solution known under the trademark Hanovia medium 4/ 91 may be used. The preferred resin content is about 35-50% by Weight but greater or lesser concentrations can be used. The metal may be present in a proportion by weight of as little as or even less of the mixed paste, or as much as 90% or even more and the paste may thus vary considerably in consistency and may even be paint-like.

When it is desired to make a sheet or strip of an alloy of a platinum-group metal, the alloying element may be introduced in a variety of ways. It may formp'art of the flake powder, for example, by simply mixing the platinum metal flake powder with a flake or other powder of the alloying element, by forming the alloy in bulk and forming this bulk alloy into fiakepowder, by coating the platinum metal flake powder with 'the alloying element, silver-coated palladium flake powder being made, for example, by mixing palladium flake with an organic silver solution and heating to dryness and to reduce the silver compound to metal and by the reverse method of coating flake of an alloying metal with a platinum metal. Alternatively, when using a flake powder paste, the alloying element may be present in the liquid constituent of the paste, for example, as an organo-metallic derivative of an alloying metal. I

. Broadly, the thermally decomposable liquids that may be used for forming the paste include metal-bearing liquids containing metals of the platinum group, gold or silver known as liquid bright metals. One example of such a liquid is a solution of gold tertiary dodecyl mercaptan in heptane, containing 30% gold. Thus, the metal in the liquid can be the same as that of the flake and it will then merely unite with the flake in the sintering process but it can also be different and becomes alloyed with the' metal of the flake and in so doing may reduce the minimum sintering temperature required.

According to a further feature of the invention, the mechanical properties ofvthe sheet or strip of platinumgroup metal are modified by the inclusion of essentially a s earer? a in acetone. The presence of an organic solvent is particularly desirable owing tothe fact that the flake powder commonly contains a small amount of an organic lubricant such as stearic acid and is thus hydrophobic.

The products of this invention are particularly useful for the manufacture of crucibles of a pure platinum-group metal or an alloy thereof, which are sufliciently strong to withstand temperatures of 1000 C. and above.

The following examples illustrate the invention:

EXAMPLE I A paste consisting of 86% platinum flake powder suspended in a resin solution sold under the trademark Hanovia medium 4/91 containing 35% by weight of resin was scraped into a 6.35 x 3.8 cm. open brass mold of 0.12

cm. thickness clamped to an unglazed porcelain plate.

The assembly was heated to C. for 1 hour, the brass mold was then removed and the compact and basewere then fired at 1000 C. for 30 minutes in air. The resulting compact was cold rolled to 0.036 cm. inthickness and annealed for 15 minutes at 1200? C. and finally rolled to 0.025 cm. in thickness. Tensile tests were carried out on this platinum strip and were'compared with those of a similarly cold worked strip from cast metal. After 100 hours at 1200 C., these were as follows:

Max. Stress, Elongation,

t.s.i.* Percent Strip from cast metal 7. 2 22 Strip from flake powder l0. 7 28 T.s.i.=long tons per square inch.

EXAMPLE II A paste consisting of palladium flake powder suspended in Hanovia medium 4/ 9.1, which was diluted with an equal volume of an organic solvent known under the trademark Hanovia Thinning Essence No. 4 to contain 17.5% resin, was scraped into a copper mold 6.35 cm. by 1.9 cm. and 0.63 cm. in thickness and clamped to a plate of alumina, sold under the trademark Sintox. The assembly was heated to 200 C. over several hours. The compact was then removed from the mold, sintered for one hour in air at 1200 C. and cooled in an atmosphere of nitrogen. The sintered compact was reduced by 28% in thickness by cold rolling. It was annealed for 30 minutes at 1200 .C. in air and this was followed-by cooling in nitrogen. It

was finally cold rolled to a thicknessof 0.12 mm. The recrystallization temperature of this strip appeared to be between 1000 C. and -1200 C. A similarly cold worked strip from cast metal had a recrystallization temperature between 600 C. and 800 C. a

EXAMPLE III This example illustrates the formation of a strip of a palladium-platinum alloy:

One part of palladium flake powder was mixed with three parts of platinum flake powder into a paste with the EXAMPLE IV The following is an example of the formation of a compact of platinum alloyed with gold:

0.1 g. of gold tertiary-dodecyl mercaptan in heptane, containing 30% by weight of gold was mixed with 3 g. platinum flake powder and 0.6 g. of Hanovia 4/91 solution. The resultant paste was spread on a support of Sintox alumina and was heated at 1200 C. for 30 minutes. The resulting compact, which was 0.12 mm. thick and contained 1% gold and 99% platinum, was suitable for cold working into an alloy strip.

EXAMPLE V This example illustrates the production of platinum strip made both from a paste of flake platinum powder and from the pressed dry flake and compares the high temperature mechanical properties of these products made in accordance with the present invention with those of strip made from pressed granular powder and from melted and cast ingots.

The flake powder was prepared from granular platinum powder obtained by the reduction of platinum-ammonium chloride in air at 600 C. and by grinding the resulting low temperature sponge to powder in an automatic pestle and mortar disposed to rotate about eccentrically placed vertical axes.

The granular platinum powder was sieved to yield a fraction the particles of which passed through a mesh of aperture width 152 microns. This fraction had a bulk density of 7.3 g./cm. and an average particle diameter, determined by the Fisher sub-sieve sizer method of 7.6 microns. The powder was converted to flake form by ball-milling a 622 g. batch for hours at 60 r.p.m. in a 4 /2 liter porcelain jar with 4500 g. of 6.3 mm. diameter steel balls and 1 g. of powdered stearic acid. The flake powder had a bulk density 3.45 g./cm.

The paste compacts were made from a paste consisting of the flake mixed with a medium comprising equal parts by weight of alkaline condensed methanol methyl cyclohexanone polymer and toluene in the proportion of 9 g. of medium to 100 g. of platinum flake powder. The paste was placed in an open, steel, split mold with a cavity 6.3 x 1.8 x 1.2 cm. deep, clamped to a flat plate of an alloy of 76% nickel, chromium and the balance mainly iron. Filling of the mold was aided by vibration at 50 c.p.s. which caused the paste to flow and, when the mold was full, vibration was continued for 5 minutes to release entrapped air bubbles. The filled mold was slowly heated to 100 C. and held at that temperature for one hour, was then heated at 200 C. for one hour and, at this stage, the mass of paste in the mold was compressed by hand by means of a flat metal plate the same size as the mold opening. The mold was then heated for a further minutes at 200 C. and allowed to cool. When cold, the mold was removed from the now compacted mass of paste which was then heated for 2 /2 hours at 250 C.- 300 C. to volatilize the resin. The compacts made in this way were sintered for 2 hours in air at 1100 C., at which stage they were approximately 0.9 cm. in thickness. The sintered compacts were hot forged at approximately 1000 C. to a thickness of about 0.5 cm. and edge defects were removed by filing and they were then cold rolled to yield strip of 0.05 cm. thickness.

The pressed flake compacts were made in a conventional steel pressing mold with a 5 x 1.2 cm. cavity. One hundred grams of the flake powder were gently tapped into the mold cavity and pressed at 25 long tons per square inch (ton/in?) in a hydraulic press. This produced compacts of approximately 0.9 cm. thickness which were sintered at 1100 C. in air for 2 hours and processed to strip by the same procedure as the paste compacts.

Similar strips were made from pressed granular platinum powder using the same procedure as that adopted for the pressed flake powder and in addition strips were made from melted and cast ingots.

6 Stress-rupture tests were then carried out on 3.2 mm. wide specimens sheared from. the cold rolled platinum strip. All tests were at a temperature of 1450" C. The results obtained were as follows:

Stress-rupture lives in hours of platinum strip prepared as indicated Pressed Paste of Pressed Melted Stress, lb./m. flake flake granularand east powder powder powder ingots The marked superiority of the strips made from flake platinum powder is immediately apparent.

EXAMPLE VI Thoriated platinum strip was prepared by forming a slurry of platinum flake in an acetone solution containing 22.7% by weight of thorium nitrate, drying the slurry, forming a compact by pressing in a hydraulic press and then sintering and working all as described in Example V. The product contained 0.3% by weight of thoria (Strip A).

Comparative samples were also made by thoriating granular platinum powder in the same way as above (Strip B), and by making a strip from the granular powder obtained from the thermal decomposition of ammonium chloro-platinate which had previously been treated with an aqueous solution of thorium nitrate to give a thoria content of 0.3% by weight Strip C).

The stress-rupture lives in hours carried out at 1450 C. on 3.2 mm. wide specimens at 400 pounds per square inch were 27.5 hours for strip B and 7 hours for strip C while strip A using flake powder had not ruptured after 406 hours. Additional stress-rupture data with regard to the thoriated platinum strip made with flake powder is contained in the following table:

The present invention is particularly applicable to the production of platinum-group metal sheet and strip and objects such as crucibles, dishes and the like made from said sheet and strip. Specifically, for the purpose of the present invention, the platinum-group metals include those platinum-group metals considered by the art to be malleable, alloys of said platinum-group metals with each other and with other metals and dispersion-hardened platinumgroup metals and alloys thereof. The products formed in accordance with the present invention can be used in the manufacture of glass working equipment and, in general, in the manufacture of structures subjected in use to the effects of ultra-high temperatures and/ or media which are corrosive to the more common metals.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered amour? 7 to be within the purview and scope of the invention and appended claims.

I claim:

1. The process for producing a metallic sheet product containing about 0.1% up to about 5%, by vo dispersed, hard, metal oxide phase, which com; ing metallic llake powder containing up to about 50%, by weight, of metal from the group consisting of gold, silver, nickel and cooper and the balance essentially plati group metal with an organic solvent solution of a metal salt decomposable to said metal oxide to cause dispersion of said metal salt throughout said flake powder, removing said organic solvent from the resulting mixture, compacting the resulting treated flake powder, sintering the resulting compact at a temperature of at least about 800 C. to form a sintered compact having about 0.1% to about 5%, by volume, of a hard metal oxide phase dispersed therethrough, and working the sintcred compact into sheet form to provide a sheet product having very substantially higher strength at elevated temperatures as compared to a similar product produced by conventional melting and Working procedures.

2. The process for producing a metallic sheet product containing about 6.1% up to about 5%, by volume, of a dispersed, hard, metal oxide phase which comprises mixing metallic flake powder containing up to about 50%, by Weight, of metal from the group consisting of gold, silver, nickel and copper and the balance a metal froi the group consisting essentially of platinum, palladium and rhodium with an organic solvent solution of a metal salt decomposable to a hard metal oxide from the group consisting of thoria, zirconia, alumina, beryilia, yttria, ceria and lanthana with said metal salt being in an amount suiiicient to provide about 0.1% to about 5%, by volume, of said hard metal oxide in said flake metal powder, removing said organic solvent, compacting the resulting treated flake powder, sintering the resulting compact at a temperature of at least about 800 C. to form a sintered compact having a hard metal oxide phase dis persed therethrough, and working the sintered compact into sheet form to provide a sheet product having very substantially higher strength at elevated temperatures as cient to pro: do about 9.1% to about 5%, by volume, of thoria metal powder upon decomposition of said tering the resulting o ed compact having thoria dispersed thereand working the sintered compact into sheet form a sheet product having very substantially higher leveled temperatures as compared to a simit produced by conventional melting and worlo 3 wherein the fialte metal powder consists essentially of metal from the group consisting of platinum, palladium and rhodium.

5. The process according to claim 4 wherein the fake metal powder consists essentially of platinum.

References Cited in the file of this patent UNITED STATES PATENTS Smithells Aug. 26,1946 Beresford July 12., 1949 Streicher luly 3, 1956 Mott May 14, 1957 FOREIGN PATENTS Great Britain Nov. 1, 1950 Great Britain Aug. 13, 1958 OTHER REFERENCES I ones: Fundamental Principles of Powder Metallurgy, Edward Arnold Publishers, London, 1960, pp. 264, 206.

t a temperat're of at least about SSS C. to

f/r/{fj/f UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,166,417 January 19, 1965 Peter Edward Gainsbury the above numbered patd that error appears in s Patent should read as It is hereby certifie nd that the said Letter ent requiring correction a corrected below.

Column 2, line 51, for "piaste" read paste column 6, line 35, for "Strip C)" read (Strip C) same column line 4 thereof, for "320.5"

6, second table, second column, read 320.25 column 7, line 9, for "cooper" read copper column 8, line 32, for "Beresford" read Middleton Signed and sealed this 6th day of July 1965.,

' (SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,166 ,417 January 19 1965 Peter Edward Gainsbury It is hereby certified that error appears in the above numbered patent requiring correct-ion and that the said Letters Patent should read as corrected below Column 2, line 51, for "piaste" read paste column 6, line 35, for "Strip C)" read (Strip C) same column 6, second table, second column, line 4 thereof, for "$20.5" read 320.25 column 7, line 9, for "cooper" read copper column 8, line 32, for "Beresford" read Middleton Signed and sealed this 6th day of July 1965,

' (SEAL) Attest:

EDWARD J. BRENNER Attesting Officer 

2. THE PROCESS FOR PRODUCING A METALLIC SHEET PRODUCT CONTAINING ABOUT 0.1% UP TO ABOUT 5%, BY VOLUME, OF A DISPERSED, HARD, METAL OXIDE PHASE WHICH COMPRISES MIXING METALLIC FLAKE POWDER CONTAINING UP TO ABOUT 50%, BY WEIGHT, OF METAL FROM THE GROUP CONSISTING OF GOLD, SILVER, NICKEL AND COPPER AND THE BALANCE A METAL FROM THE GROUP CONSISTING ESSENTIALLY OF PLATINUM, PALLADIUM AND RHODIUM WITH AN ORGANIC SOLVENT SOLUTION OF A METAL SALT DECOMPOSABLE TO A HARD METAL OXIDE FROM THE GROUP CONSISTING OF THORIA, ZIRCONIA, ALUMINA, BERYLLIA, YTTRIA, CERIA AND LANTHANA WITH SAID METAL SALT BEING IN AN AMOUNT SUFFICIENT TO PROVIDE ABOUT 0.1% TO ABOUT 5%, BY VOLUME, OF SAID HARD METAL OXIDE IN SAID FLAKE METAL POWDER, REMOVING SAID ORGANIC SOLVENT, COMPACTING THE RESULTING TREATED FLAKE POWDER, SINTERING THE RESULTING COMPACT AT A TEMPERATURE OF AT LEAST ABOUT 800*C. TO FORM A SINTERED COMPACT HAVING A HARD METAL OXIDE PHASE DISPERSED THERETHROUGH, AND WORKING THE SINTERED COMPACT INTO SHEET FORM TO PROVIDE A SHEET PRODUCT HAVING VERY SUBSTANTIALLY HIGHER STRENGTH AT ELEVATED TEMPERATURES AS COMPARED TO A SIMILAR PRODUCT PRODUCED BY CONVENTIONAL MELTING AND WORKING PROCEDURES. 